Recently, as the performances of computers have been further enhanced, a working environment that enables a person to create highly realistic computer graphics has almost been established. Among other things, the performance of a graphic processing unit (GPU) that is dedicated to graphic processing has been improved so significantly these days that a GPU with the ability to generate a moving picture in real time through computations is easily available now. Meanwhile, computer graphics have been used in more and more occasions lately and are now seen in any of various kinds of media that include not just movies but also ads on TV, the Internet and magazines, merchandise catalogs and simulation or reproduction video in news programs.
Specifically, in a merchandise catalog, an image or video representing a “product”, which is an existent object, by computer graphics is placed. A number of advantages are achieved by using computer graphics. First of all, by using computer graphics, various constraints that would be imposed if the actual product had to be set in the right place for shooting can be eliminated. For example, if a running car needs to be filmed, it must be determined first where the car should run. In that case, in order to avoid ruining the advertising effect, the best location that will meet particular conditions needs to be found. On top of that, if the product should be actually shot, the weather would also be an important factor. Nevertheless, a prolonged shooting session would increase the overall cost and could affect the sales plan of the product. Furthermore, sometimes the advertising effect can be increased much more significantly by using video representation rather than shooting the actual product. For instance, even if video needs to be produced from an angle at which it would be dangerous to shoot the actual product, such video may be produced easily by using computer graphics.
Lately, various methods for generating computer graphics have been developed one after another. A so-called “texture mapping” technique is known as one of those various methods. The “texture mapping” is a technique for increasing the degree of reality of the appearance of an object represented by a computer by expressing the surface pattern and gloss of the object with more fidelity. That is to say, with the texture mapping technique, the “reality” of the object appearance can be increased so much that the object may look as if it were a real one. In this case, the “texture” is a generic term that refers collectively to the surface pattern, gloss and other looks of a given object. A texture mapping-related technology is disclosed in Non-Patent Document No. 1, for example.
FIG. 20 illustrates an exemplary texture mapping process. If an appropriate object surface texture 1002 is attached to a given object (e.g., a circular cylinder in this example) 1001 so as to fit its surface perfectly, a highly realistic image 1003 can be generated.
According to the texture mapping technology, when a texture represented as a two-dimensional image is attached to a three-dimensional object image, the luminance value of a normally rectangular texture image is changed according to the three-dimensional shape to represent. In the example illustrated in FIG. 20, the luminance value of the rectangular texture image 1002 is changed according to that of the side surface of the circular cylinder 1001. As a result, in the image 1003 thus generated, the luminance value of the rounded texture image that has been attached to the circular cylinder 1001 changes according to the shape of the circular cylinder 1001. As a result, unnaturalness can be eliminated from the appearance of the object represented. That is to say, a highly realistic image 1003 can be obtained.
A computer graphics image is supposed to be generated by getting the light that has been emitted from a light source reflected by a given object and by calculating, using a computer, the luminance value of a part of that light that has reached a particular viewpoint. To give a realistic texture to the surface of an object represented, ordinarily an image that has been actually shot with a digital camera or any other image capture device is used as a texture image and the luminance value of that actual shot is used.
Nevertheless, as a result of attempts to meet ever-growing demands for realistic appearance these days, it has turned to be more and more apparent that the resolution limit should be reached sooner or later if everything was calculated model based. For one thing, as the number of pixels to process has skyrocketed to meet the users' high-definition image expectations, the computational load has also increased tremendously. As a result, more and more people now know that there are some limits to the representation ability of the model based method.
Thus, considering the recent hugely expanding range of applications of computer graphics and rising demands for even more realistic representations, an image based technique, by which the object is actually shot or measured and used for texture mapping, has been used more and more often these days. And some people now regard the image based method as an indispensable technique for generating computer graphics.